Green Roof Resource

It’s been awhile since I’ve looked at the new green roof literature. There have been several papers on green roofs published within the last 6 months including reviews, thermal performance, and stormwater management. Summarized below are 2 papers focusing on the thermal performance of green roofs. It is exciting to see a focus on both the individual building and city scale benefits in the literature.

A recently published paper in Building and Environment by Eleftheria Alexandri and Phil Jones evaluated the temperature decrease in urban canyons from the application of green roofs and green walls in 9 cities [1]. Through a two dimensional model of an urban canyon, the researchers show that green roofs and green walls can reduce urban temperatures. Green walls contribute more to local urban canyon temperature reductions than green roofs while green roofs provide greater temperature reduction to the surrounding urban areas. Additionally, the modeling shows that cities in humid climates can also benefit from vegetated surfaces. The combination of green walls and green roofs can reduce or eliminate cooling loads for buildings depending upon a city’s climate.

In Renewable Energy, A. Spala et al modeled an office building using TRNSYS to determine a green roof’s impact on the heating and cooling load of the building [2]. TRNSYS is a commercially available energy system simulation tool originally developed by University of Wisconsin at Madison Solar Energy Lab and the University of Colorado Solar Energy Applications Lab. TRNSYS is based on the Fortran language and can be modified to describe a particular building. While the authors state assumptions regarding thermal performance of materials on the green roof, it is not clear what assumptions were made regarding the thermal performance of the soil media and plant material. Significant reductions in cooling loads were observed for the two-story building on both the top floor (27-58% reduction) and the entire building as well (15-39% reduction). The effect on heating loads was less clear.

References
[1] Alexandri, E; and P Jones. 2008. “Temperature decreases in an urban canyon due to green walls and green roofs in diverse climates,” Building and Environment, 43: 480-493.
[2] Spala, A; Bagiorgas, HS; Assimakopoulos, MN; Kalavrouziotis, J; Matthopoulos, D; and G Mihalakakou. 2008. “On the green roof systme. Selection, state of the art and energy potential investigation of a system installed in an office building in Athens, Greece,” Renewable Energy, 33:173-177.